1. Field of the Invention. This invention is related to the practice and teachings of the helicopter art.
2. Description of the prior Art. Example of helicopter teachings pertinent to this invention and which have been known prior to this invention are found in the disclosures of the following patents.
U.S. Pat. No. 2,369,652 provides an anti-torque air screw having an axis of rotation at right angle to the aircraft longitudinal axis. The air screw is located within fuselage. Louvers consisting of controllable vertical slates, which are closed when the anti-torque air screw is not operating, are located on the opposite side of the fuselage and relatively in line with the air flowing by the air screw.
U.S. Pat. No. 3,047,254 relates to yaw control means and U.S. Pat. No. 3,026,068 relates to automatic yaw controls means, both are for a helicopter. Both aforementioned patents disclose a source of high velocity air which is conducted to a position spaced from the center of gravity of the vehicle to the aft end of a tail boom and there directed in generally three different directions, either simultaneously or singly, to provide yaw control forces or forward thrust forces. The high velocity air, after passing the direction guides, discharges into the atmosphere. The source of high velocity air is a forward mounted fan aligned with the longitudinal axis of the helicopter and at a right angle to the plane of rotation of the rotary wings.
U.S. Pat. No. 3,059,877 discloses an anti-torque effect which is generated by passing the downwash of the rotor over the fuselage which has longitudinal slats emitting pressurized air from within the fuselage. The jets retard the downwash on one side of fuselage and accelerate the downwash on the other side and the two different velocities of flow cause a net force on the fuselage counter to the main rotor torque.
U.S Pat. No. 3,351,304 discloses a vertical-lift forward-thrust aircraft. An internal turbofan engine, which axis is aligned with the longitudinal axis of the aircraft, provides air to an aft aerodynamic valve.
U.S. Pat. No. 3,510,087 discloses an air coupling system for a helicopter which ejects a small portion of the air mass flow at the tail of the helicopter in a direction to counteract the torque created by the air coupling system. The larger balance of the air is directed downwardly, after passage through a turbine, thereby creating a direct lift independent of the rotor lift.
U.S. Pat. No. 3,807,662 discloses a main rotor-driven axial compressor fan feeding a variable-geometry nozzle at the end of an enlarged duct extending from a diffuser located immediately adjacent the fan, generating either an anti-torque moment or a forward propulsion thrust, or both. The fan is aligned with the longitudinal axis of the helicopter.
U.S. Pat. No. 4,200,252 discloses an helicopter anti-torque system consisting of slots extending longitudinally along the tail boom and a sheet of air is continuously discharged from the slots tangentially to the surface of the tail boom. The discharged area is supplied by a fan within the fuselage which directs a stream of air rearwardly into the tail boom. The tail boom is provided at its rear end with a laterally disposed aperture through which some of the fan-supplied air is discharged to create a direct jet thrust. The flow through the aperture is throttled to vary the anti-torque moment for trim and maneuvering.
British Patent No. 577,524 discloses an improved anti-torque propeller externally located aft on the fuselage.
British Patent No. 703,067 discloses a duct connecting an outlet opening at the surface of an aerofoil with a forwardly directed intake which opens at or in advance of the leading edge port of the aerofoil so that air entering the intake in consequence of forward motion of the aircraft issues from the outlet and produces a control force.
French Patent No. 1,298,518 discloses a centrally located, vertical fan and a long duct to vertical aft openings that direct the exiting air.
French Patent No. 883,462 discloses a duct pressurized from a source of air at the forward end, and two exists at the aft end. The exits located on the left and right sides of the fuselage are of different sizes, the left exit larger than the right exit. The right exit has a vertical flapper type shutter which can close or open to provide a force to the left. The two openings can work together for autorotation. For normal powered flight, the left exit operates independently of the right exit.
German Patent No. 1,933,353 discloses means for providing auxiliary forward thrust and yaw control. The main rotor is driven by air pumped from an engine to a rotor and out a blade tip producing little torque.
The aforementioned art is generally directed towards an anti-torque system and/or yaw control which also may effect forward thrust and/or lift and other flight characteristics. Generally the prior art performance is less than desireable and attempts are constantly being made to improve the prior art. The present invention, which is an improvement over the prior art, has advantages not obtainable via the prior art. The present invention has an aft mounted horizontal fan which is submerged within a fuselage mounted plenum. The upward facing plenum has two controllable ports for counter torque control, fuselage pitch control, and yaw control. The two controllable ports are used in combination or separately to achieve the desired control of torque, pitch and yaw.
Compared to a conventional tail rotor present invention has numerous advantages. These are as follows: The mounted horizontally rotor within the fuselage mounted plenum protects ground personnel from dangerous physical contact with a conventional tail rotor. Further said horizontally rotor is protected from the following: terrain strikes resulting from high flair angle and slope landings; vertical objects such as trees, walls, poles and the like near a landing or take off sites; foreign objects such as stones, hardware and the like being trapped in the tail rotor tip vortices and drawn into the rotor; and in-flight wire strikes. The main rotor is protected from stones, parts and debris because the horizontal rotor will not pass said stones, parts and debris to the main rotor.
Further the horizontal fan operating within the plenum's upward facing entrance reduces acoustic, radar, visual and infrared signature compared to a vertical tail rotor fan. Also the horizontal fan operating at the entrance to the plenum has little variation of inflow velocities across the plane of the tail rotor and therefore does not exhibit blade stall or compressibility effects associated with a free vertical tail rotor in forward flight. Still further the horizontal fan eliminates the high speed forward flight velocity limitations generally associated with the free vertical rotor; i.e. vibrations, stability and control problems, high stresses, and high blade flapping. Also still further the horizontal fan, being parallel to the main rotor plane, can operate under and within the main rotor radius thus shortening the fuselage length and thereby reduce the overall weight. Still further additional vertical lift is generated at the entrance, which may be suitable curved, to the plenum as air is drawn into the plenum. Still further as the plenum has horizontal vanes at the exit ports, in operation it can produces pitch attitude control in hover and forward flight. Also the horizontal fan generates torque which is counter to the torque produces by the main rotor. And further the increased fuselage width which may be necessary to accommodate the horizontal fan, may be used to contain additional items.